1. Field of the Invention
The present invention relates to an electromagnetic lens shutter apparatus for a camera. More particularly, this invention relates to an electromagnetic lens shutter apparatus in which lens shutter blades are operated electromagnetically.
2. Description of the Prior Art
Generally, the opening and closing functions of shutter blades are carried out by controlling a direction and a time of an electrical current which flows through an electromagnet in an electromagnetic shutter apparatus. Such an electromagnetic shutter apparatus has a simple construction compared with a mechanical shutter which uses a mechanical spring force to effect the opening and closing functions of shutter blades.
U.S. Pat. No. 4,881,093 discloses an electromagnetically operated shutter assembly for a camera which includes permanent magnets which are affixed to shutter blades. An electromagnetic field is generated by a number of armatures which interact with the permanent magnets to cause the shutter blades to move between open and closed positions. The configurations of the permanent magnets and armatures permit the blades to be held in the open and closed positions without the further application of current to the armatures. Also, the permanent magnets are levitated by the electromagnetic field in order to facilitate movement of the shutter blades between the opening and closing positions. However, such a shutter cannot be applied to an automatic focusing and exposure camera.
Japanese Patent Publication No. 90-33130 describes an electromagnetically operated shutter mechanism in which a first moving coil member for moving a shutter blade between an affixed permanent magnet and a yoke at an opposing position of the permanent magnet and a second moving coil member for deciding an open degree of the shutter blade are provided. An operation of both moving coil members is carried out at a predetermined time difference, so that an automatic exposure is effected. However, since the shutter in this manner does not have an automatic focusing function, it is applied only to a simple fixed focus camera and cannot be applied to a zoom camera commonly used at the present time.